In conventional machine tools, such as lathes, a workpiece is securely supported in a chuck during the machining operation. The chuck is mounted on one end of a spindle and the spindle is rotated so that a tool may be brought into contact with the rotating workpiece. The tool has a cutting edge which cuts into the workpiece to remove material so that the workpiece can be machined to the desired shape and size. The material thus cut from the workpiece by the tool may take the form of discrete chips. If desirable, a liquid coolant may be used to lubricate the cutting edge of the tool and to prevent heat buildup.
To automate the machining operation, it is desirable to provide an automatic chuck which can be controlled to selectively grip or release a workpiece disposed within the jaws of the chuck. To more fully automate the machining operation, however, it is also desirable to provide a workpiece transfer apparatus for loading workpieces into the chuck before the machining operation is performed and for unloading the workpieces from the chuck after the machining operation has been completed. The workpiece transfer apparatus may pick up unmachined workpieces from a loading station such as a chute or bin adjacent to the machine tool. In addition, the workpiece transfer apparatus may unload workpieces from the chuck and transfer them to an unloading station such as a chute or bin adjacent to the machine tool.
Conventional workpiece transfer devices may include a moveable shaft having a workpiece gripping mechanism mounted on one end thereof. Such shafts are typically moveable axially along the shaft axis, known in the art as the "Z direction", and may also be moveable rotationally about the shaft axis, known in the art as the "C direction". Such workpiece transfer devices may include a motor for providing the rotational movement in the C direction and a hydraulic or pneumatic cylinder for advancing and withdrawing the shaft along its axis in the Z direction. These transfer devices therefore require both an electrical power source for the rotational motor and a separate hydraulic or pneumatic power source for moving the shaft axially.
Another type of workpiece transfer device is disclosed in U.S. Pat. No. 4,646,422 to McMurtry. The device of the McMurtry patent comprises a transfer mechanism including a shaft supported at both ends for rotation thereof. An arm is supported on the shaft for movement along the axis of the shaft but is fixed against rotation relative to the shaft. A first motor rotates the shaft and a second motor rotates a threaded rod inside the shaft to move the arm in an axial direction along the shaft. The shaft, however, extends substantially between the tool and chuck of the machine and thus limits access to the machining area. In addition, the workpiece transfer mechanism is subjected to chips and coolant produced by the machining operation.
Another type of workpiece transfer device is disclosed in U.S. Pat. No. 4,458,566 to Tajima. The Tajima patent discloses a device having an arm secured to the end of a moveable shaft. The shaft of the Tajima patent is moveable both axially and rotationally about its axis. However, rotational movement is provided by a threaded rod which is mounted perpendicularly to the arm axis and, as such, is limited to rotation through an arc determined in part by the length of the rod. Such limited rotational movement limits the loading and unloading capability of the arm.
The chips and coolant produced by the machining operation are often expelled from the vicinity of the tool in unpredictable trajectories. Moreover, errant chips and coolant can be detrimental to the machine tool. For example, chips may interfere with the operation of the gripper devices used for loading and unloading workpieces. Thus, it is desirable to confine chips and coolant to the immediate vicinity of the machining operation.
The workpiece gripping mechanisms of conventional workpiece transfer devices typically include a three-jawed chuck and a pusher plate spring-loaded between the jaws. The workpieces are picked up from an opening at the end of a declining input chute by the gripping mechanism and are transferred to the chuck. A workpiece is positioned at the opening of the chute and is restrained from falling through the opening by a moveable shutter. The gripping mechanism is moved towards the workpiece, the shutter is opened and the pusher plate engages the workpiece. The jaws are then closed and the workpiece can be removed from the chute.
More workpieces may be restrained further up the input chute so as not to interfere with the operation of the three jaws of the gripping mechanism. The workpieces may be restrained by two retractable gates operating in an escapement fashion so as to allow only one workpiece at a time to advance to the opening. Workpiece transfer devices of this type thus require the provision of a moveable shutter and two retractable gates which adds to the expense and complexity of the transfer apparatus.
It is therefore an object of the present invention to provide an improved workpiece transfer apparatus for machine tools.
It is still another object of the present invention to provide an improved workpiece transfer apparatus which allows full access to the machining area and which has improved mobility.
It is yet another object of the present invention to provide an improved machine tool which provides improved confinement of chips and coolant produced during the machining operation.
It is yet another object of the present invention to provide an improved work transfer apparatus having fewer actuated components.